Method for using reversible phase oil-based drilling fluid
Invert emulsion compositions including an oleaginous, a non-oleaginous and an amine surfactant that are useful in the oil and gas well drilling art are disclosed. The amine surfactant is selected so that the invert emulsion can be converted form a water-in-oil type emulsion to a oil-in-water type emulsion upon the protonation of the amine surfactant. Deprotonation of the amine surfactant reverses the conversion. This solution also permits the conversion of oil-wet solids in the fluid into water-wet solids.
1. A method of gravel packing a downhole area of a subterranean well, said method comprising:
a) forming a mixture of a gravel packing material and an invert emulsion drilling fluid, wherein said fluid includes: an oleaginous fluid; a non-oleaginous fluid; an amine surfactant having the structure
wherein R is a C 12 –C 22 aliphatic hydrocarbon; R′ is an independently selectable from hydrogen or C 1 to C 3 alkyl; A is NH or O, and 1≦x+y≦3;
b) injecting said mixture of gravel packing material and invert emulsion into a subterranean well so as to gravel pack the downhole area; and
c) adding acid to said invert emulsion drilling fluid so as to change the oil-wet gravel packing materials into water-wet gravel packing materials and;
d) washing said well with an aqueous based wash solution.
2. The method of claim 1 wherein said oleaginous fluid comprising from 5 to about 100% by volume of the oleaginous fluid of a material selected from a group consisting of esters, ethers, acetals, di-alkylcarbonates, hydrocarbons, and combinations thereof.
3. The method of claim 1 wherein said non-oleaginous liquid is an aqueous liquid.
4. The method of claim 3 wherein said aqueous liquid is selected from the group consisting of sea water, a brine containing organic or inorganic dissolved salts, a liquid containing water-miscible organic compounds, and combinations thereof.
5. The method of claim 1 wherein said amine surfactant is selected from diethoxylated tallow amine; diethoxylated soya amine; N-aliphatic-1,3-diaminopropane wherein the aliphatic group is a C 12 to C 22 hydrocarbon; or combinations thereof.
6. A method of gravel packing a downhole area of a subterranean well, said method comprising:
a) forming a mixture of a gravel packing material and an invert emulsion drilling fluid, wherein said fluid includes: an oleaginous fluid; a non-oleaginous fluid; an amine surfactant having the structure
wherein R is a C 12 –C 22 aliphatic hydrocarbon; R′ is an independently selectable from hydrogen or C 1 to C 3 alkyl; A is NH or O, and 1≦x+y≦3;
b) injecting said mixture of gravel packing material and invert emulsion into a subterranean well so as to gravel pack the downhole area; and
c) acidifying said invert emulsion drilling fluid so as to change the oil-wet gravel packing materials into water-wet gravel packing materials and;
d) washing said well with an aqueous based wash solution.
7. The method of claim 6 wherein said fluid is acidified by carbon dioxide from the formation.
8. The method of claim 6 wherein said fluid is acidified by hydrogen sulfide from the formation.